Doosan D20G, Service Manual

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G424F(FE) Service Manual Chapter 5. Engine Management System (EMS) 153
Other system features include:
Tamper-Resistance
Special tools, equipment, knowledge, and
authorization are required to effect any changes to
the MI-07 system, thereby preventing unauthorized
personnel from making adjustments that will affect
performance or emissions.
Diagnostics
MI-07 is capable of monitoring and diagnosing
problems and faults within the system. These
include all sensor input hardware, control output
hardware, and control functions such as closed-loop
fuel control limits and adaptive learn limits. Upon
detecting a fault condition, the system notifies the
operator by illuminating the MIL and activating the
appropriate fault action. The action required by each
fault shall be programmable by the OEM customer
at the time the engine is calibrated.
Diagnostic information can be communicated
through both the service tool interface and the MIL
lamp. With the MIL lamp, it is possible to generate a
string of flashing codes that correspond to the fault
type. These diagnostics are generated only when
the engine is not running and the operator initiates a
diagnostic request sequence such as repeated
actuations of the pedal within a short period of time
following reset.
Limp Home Mode
The system is capable of "limp-home" mode in the
event of particular faults or failures in the system. In
limp-home mode the engine speed is approximately
1000 rpm at no load. A variety of fault conditions can
initiate limp-home mode. These fault conditions and
resulting actions are determined during calibration
and are OEM customer specific.
Service Tool
A scan tool/monitoring device is available to monitor
system operation and assist in diagnosis of system
faults This device monitors all sensor inputs, control
outputs, and diagnostic functions in sufficient detail
through a single access point to the SECM to allow
a qualified service technician to maintain the system.
This Mototune software (licensed by Mototron
Communication) is secure and requires a crypt-
token USB device to allow access to information.
LPG Fuel System Operation
The principles outlined below describe the operation
of MI-07 on an LPG fuel system.
An LPG fuel system consists of the following
components:
• Fuel filter (supplied by customer)
• Electric fuel lock-off solenoid valve
• Fuel pressure regulator/vaporizer
• Gas/Air mixer
• Miscellaneous customer-supplied hoses and
fittings
Fuel is stored in the customer-supplied LPG tank in
saturated liquid phase and enters the fuel system
from the tank as a liquid and at tank pressure. Fuel
passes through a high-pressure fuel filter and lock-
off solenoid, and is then vaporized and regulated
down to the appropriate pressure to supply the
mixer. The regulator controls the fuel pressure to the
gas/air mixer. The mixer meters fuel delivery based
upon airflow into the engine.
SECM
The Small Engine Control Module (SECM) controls
the LPG lock-off solenoid valve. The lock-off
solenoid is energized when fueling with LPG and the
engine is turning. The lock-off is de-energized when
engine rpm is not detected.
MI-07 LP Fuel Filter
The LP fuel filter of G424F engine is the same as
that of G424FE engine. See, “G424FE EMS
overview”
MI-07 Fuel Lock-Off (Electric)
The LP fuel lock-off of G424F engine is the same as
that of G424FE engine. See, “G424FE EMS
overview”
N-2001 Regulator/Converter
After passing through the electric fuel lock-off, liquid
propane enters the N-2001 regulator/converter
(Figure 4). The N-2001 functions as a fuel vaporizer,
converting liquid propane to vapor propane and as a
two-stage negative pressure regulator, supplying the
correct vapor propane fuel pressure to the mixer.
The regulator is normally closed requiring a vacuum
signal (negative pressure) to allow fuel to flow. This
is the second of three safety locks in the MI-07
system. If the engine stops, vacuum signal stops
and fuel flow will automatically stop when both the